Environmental Factors Influencing Hairy-Nosed Wombat Abundance in Semi-Arid Rangelands

Understanding environmental factors influencing the abundance of species is important for developing strategies to manage wildlife effectively. Long-term studies provide the most reliable information upon which to base management decisions. This is particularly important when considering threatening processes, like drought and climate change, and a species’ future security. We collected data on abundance of southern hairy-nosed wombats (Lasiorhinus latifrons) on Kooloola Station in South Australia’s Murraylands during nightly spot-lighting excursions in winter and spring between 1993 and 2014. Wombat numbers declined significantly after the early-mid 1990s, and were lowest in 2002–2003 in the middle of the millennium drought (late 1996–mid-2010). Despite an observed decline in grazing competition from domestic sheep and rabbits (Oryctolagus cunniculus) after 2003 and above-average rainfall in 5 of the next 11 years, the wombat population failed to recover to early–mid-1990s levels, remaining at approximately 50% of estimated abundance pre-drought. The study provides evidence that rainfall has a significant effect on southern hairy-nosed wombat population size, most likely through improvements in the availability of palatable plant species. Historical information suggests that there was a change in the grass and herbaceous layer on Kooloola Station in the mid-1970s from a pasture dominated by summer-germinating native grass and forb species, the natural diet of the southern hairy-nosed wombat, to one dominated by winter-germinating introduced weeds. Several consecutive years of above-average rainfall are needed before effective wombat population increase occurs and the size of yearly winter and spring rainfall events is strongly linked to population trends the following year. Historical information and first-hand observations suggest that dietary components (either native grasses or introduced weed species) and level of grazing competition may also interact to affect wombat survival and population recovery from drought, although this requires further testing. Together with rainfall, these factors have important implications to develop appropriate conservation and management strategies for this species in a changing climate likely to be dominated by increased drought frequency and duration.